A Surplus Production Model Considering Movements between Two Areas using Spatiotemporal Differences in CPUE: Application to Sea Ravens Hemitripterus villosus off Fukushima as a Practical Marine Protected Area after the Nuclear Accident

Abstract

Although the number of marine protected areas (MPAs) for stock management has increased, movements or differences in population structure of a target species between an MPA and surrounding fishing areas have rarely been considered in stock biomass estimations. We developed a surplus production model considering seasonal movements between two areas; the model was applied to Sea Ravens Hemitripterus villosus off Fukushima, where almost all fishing has been prohibited since the 2011 accident at the Fukushima Dai‐ichi Nuclear Power Plant. We predicted future biomass by using CPUE data from coastal gill‐net fishing and offshore bottom trawl fishing in 2000 to 2009. The model reflected the seasonal coastal–offshore movements of Sea Ravens well, and it predicted increasing Sea Raven biomass in both areas, which was validated by the CPUEs observed after 2010—including those for trial bottom trawl fishing that occurred within limited offshore areas after the accident. Our results indicate that the newly developed model incorporating seasonal movements of Sea Ravens is feasible and that the waters off Fukushima have effectively been serving as an MPA since the nuclear accident. We also demonstrated the model's applicability for estimating the optimal fishing effort and designing a new MPA for stock management that considers seasonal movements. Received August 29, 2014; accepted May 4, 2015

Effect of decreased fishing effort off Fukushima on abundance of Japanese flounder (Paralichthys olivaceus) using an age‐structured population model incorporating seasonal coastal‐offshore migrations

“…Our results support the waters off Fukushima can potentially be considered to be a successful MPA. Actually, biomass of sea raven (Shibata et al ., ) and stock size of Pacific cod off Fukushima (Narimatsu unpublished data) increased after the FNPP accident and the mean CPUE of exploited species from the trial fishing in 2012 was about three times the mean CPUE per year from 2007 to 2009 (Yamada et al ., ). These findings indicate that the effective MPA has not only influenced the abundance of Japanese flounder but also the abundance of other commercial species.…”

“…The fishing logbooks taken by the captain of each vessel included data on fishing dates, depth, longitude, latitude, net‐entering and net‐hauling times for each trawling operation, gill net length and mesh size (only for gill net fishing), and yield (nearest 0.1 kg) of 15 species for each operation. Although the number of vessels that cooperated to record the fishing logbooks was different each year, on average, 8.0% and 27.5% of gill net and bottom trawl vessels off Fukushima cooperated each year to record the data in the logbooks from January 2000 to February 2011 (Shibata et al ., ). The observed total gill net length and towing hours per month calculated from the logbooks were divided by a ratio of vessels that cooperated to record the logbooks per year to estimate total gill net length and towing hour per months of all vessels.…”

“…The observed total gill net length and towing hours per month calculated from the logbooks were divided by a ratio of vessels that cooperated to record the logbooks per year to estimate total gill net length and towing hour per months of all vessels. Because there was little difference in tonnage, engine power, gill net mesh size (only for gill net fishing), cod‐end mesh size and head rope length (only for bottom trawl fishing) between observed and unobserved vessels, the vessels that cooperated to record the fishing logbooks were assumed to be representative of all gill net and bottom trawl fishing vessels (Shibata et al ., ).…”

“…The waters off Fukushima were divided into coastal and offshore areas based on the operated depth of gill net and bottom trawl fishing. We calculated the range of depths of gill net and bottom trawl fishing operation and the areas shallower (deeper) than 78.0 m depth were defined as the coastal (offshore) area (Shibata et al ., ). In other words, gill net (bottom trawl) fishing was not carried out in the offshore (coastal) fishing area.…”

“…Recently, a spatially explicit surplus production model was developed to estimate and predict the biomass of sea raven ( Hemitripterus villosus ) after the FNPP accident considering their seasonal migrations between coastal and offshore areas off Fukushima (Shibata et al ., ). They showed that the model reflected the seasonal coastal–offshore migrations of sea raven well and predicted increasing biomass in both areas, indicating that the waters off Fukushima have effectively been serving as an MPA since the FNPP accident.…”